The present invention relates to pipe preparation machines for cutting a length of pipe, and preparing the end of the pipe to receive a welding. Where the end of a length of pipe is accessible, a cutting machine or pipe preparation machine may be fitted over the open end of the pipe. Where both ends of the pipe are welded into place, a split frame machine having an annular stationary member and an annular rotating member with both the annular members divisible into semi-circular sections is required.
To cut through the wall of a length of pipe, or to prepare the distal end of the pipe, a pipe preparation machine includes an annular portion that attaches to the outer surface of the pipe and a rotating annular portion that retains a tool for working against a surface of the pipe. Where the rotating portion of the machine rides on bearings that extend around the circumference of either the stationery member or the rotating member, the bearings must be carefully aligned so as to evenly distribute the forces applied thereto and the rotating portion rotates about the same axis that defines the center of the stationary portion. If the bearings are not properly aligned, one or more of the bearings will be subjected to excessive forces and become worn. As the bearings wear, the gearing between the rotating and stationary members will also become misaligned, with the alignment worsening as the bearings wear until failure occurs in either the bearings or the gearing.
Each of the bearings that facilitate the rotation of the rotatable member is mounted on a shaft that is in turn received in a bore in one of the stationary members. To operate properly, the forces applied to the various bearings must be balanced, which requires radial positioning of the bearings with respect to the common axis to a fraction of a thousandth of an inch. However, the bores that receive the mounting shafts for the bearings cannot be positioned to the degree of accuracy required to maintain the proper balance of forces against the various bearings. Accordingly, it has become the practice to mount the bearings on shafts having an attachment shank that is offset with respect to the portion that receives the bearing. By rotating the attachment shank within a mounting bore, the bearing can be radially moved to balance the forces thereon. This structure is more fully described in Swiatowy, U.S. Pat. No. 5,054,342 issued Oct. 8, 1991, the text of which is incorporated herein by reference.
In a split frame device such as described in the Swiatowy referenced mentioned above, both the stationary annular member and the rotating annular member are divisible into semi-circular halves which may be disassembled and reassembled around a length of pipe. As acknowledged above, the operators of such devices have difficulty in balancing of the forces on the bearings. Even after the forces have been balanced, it has been found that regardless how tightly the retaining nuts are tightened, the bearings of prior art machines tend to move out of balance over a relatively short period of time.
Each of the bearings is mounted on an off-center shaft having a threaded distal end for receiving a nut that is tightened to lock the shaft in the desired orientation. A hex screw driver is inserted into a hex bore in the end of the shaft to retain the off-center bearing in its desired orientation as the nut is tightened. It has been found, however, that as the nut is tightened the shaft will tend to rotate through a small angle regardless of the technician's efforts to resist such movement. Furthermore, split frame pipe machines typically have ten to sixteen of such bearings, and it is virtually impossible for a technician to equally balance the forces against all of the bearings. It would be desirable, therefore, to provide a pipe preparation machine for which it would be simpler to adjust the forces on the bearings thereof, and that would retain its adjustment over a longer period of time.